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The problem with pine

It’s one of our most popular timbers, used for everything from fences and floorboards to furniture and playground equipment – but pine presents an increasingly knotty problem, writes Michelle Wheeler.

Pine was the wood of choice for much of the 20th century.

In the 1950s and 1960s, Perth was growing fast.

Economic prosperity, post-war immigration and the birth of the baby boomers meant demand for housing materials was far outstripping the supply available for construction.

To meet WA’s growing demand for structural timber, swathes of Perth’s Banksia woodland were cleared to make way for large pine plantations.

Problem solved, it seemed. However, that move lay the foundations for a serious issue that wouldn’t rear its head for years to come.

The new pine plantations feeding Perth’s appetite for readily available, affordable timber were planted on top of the Gnangara groundwater system — Perth’s largest natural source of fresh water.

With the native vegetation cleared, the water table initially rose.

But as the pines grew, the water level dropped again. And it kept dropping.

The dense plantations were thirstier than the Banksia woodland they replaced, and they guzzled the rain before it could recharge the aquifer.

Reduced rainfall as a result of climate change and increased demand for water compounded the Gnangara’s woes, and groundwater levels kept falling.

Under increasing pressure to make sure Perth didn’t run out of water, the State Government began harvesting the plantations.

But the pines had already set in motion a succession of environmental impacts — both good and bad — that had fundamentally reshaped the landscape.

From deep underground to the skies above, the impact of the plantations could not be easily undone.

Carnaby’s cockatoos have switched from their traditional native diet to one focussed more on pine.

Fast food for cockatoos

If there’s one big environmental winner from the pines, it’s the Carnaby’s cockatoo.

The endangered bird, which is native to South West WA, has become increasingly reliant on the pine plantations to survive amid widespread clearing of the Swan Coastal Plain.

ECU Professor of Environmental Management William Stock says clearing the bush took away the cockatoos’ natural food source and replaced it with a new one — pine.

He says in some cases, pine plantations can produce more energy per hectare than the original banksias.

“It's an interesting one because I never expected pine to have any use whatsoever other than as a timber tree,” Stock says.

“Where I came from in South Africa they were considered to be the absolute worst of the worst.”

This concentrated food source is also easier for the birds to eat — prompting researchers to label it “fast food” for cockatoos.

“The ‘fast’ is really saying that they can also eat the seeds very quickly because they're easy to get out of the cones,” Stock says.

“Banksias are difficult, even for those birds, to actually feed quickly.”

Carnaby’s cockatoos have in fact become so dependent on pine that some environmental groups — including the World Wildlife Fund — have warned the birds could disappear from Perth’s skies if the clearing is not halted.

Biological Deserts

Cockatoos aside, pine plantations are renowned for being biological deserts.

The needles dropped by the mature trees are very different to native leaf litter and limit the native seedlings that would germinate underneath.

“Very little survives under pine, because it's a very dense canopy,” Stock says.

“You get virtually no understorey, and there are very few animals that will adapt to living in pine.

“They are very rich in tannins and various other compounds which are slow to decompose, and they're very low in nitrogen and other nutritional elements that animals would get.

“They also acidify the soil… most times that you plant pine, you basically would be losing diversity quite rapidly.

” And the effects of pine aren’t limited to the plantations themselves, with seeds easily dispersed into adjoining bushland.

ECU ecologist Dr Eddie van Etten has found invasion from Pinus radiata plantations is threatening neighbouring forest in the South West.

His research found an average of 71 pines per hectare in jarrah forests and 25 per hectare in karri forests.

“Every site we visited, there was at least a little bit of pine invasion into neighbouring bushland,” van Etten says.

“There were a few areas where there was probably as much pine as there was native eucalyptus.”

Instead, the highest levels of invasion can be found in patches of remnant wetlands.

Associate Dean Professor Ray Froend says what we’re seeing is a fundamental reduction in the amount of water in the landscape, as a result of both climate change and our own actions locally.

“It’s become drier and the vegetation needs are responding,” he says.

“In some cases, you'll lose species, and we have seen that particularly around wetlands, where we have lost species that are vulnerable to drier conditions.”

Plantations of pine trees make it hard for anything else to grow.

Jobs and timber growth

Of course, it’s impossible to ignore the economic value of WA’s forestry industry.

A 2017 report puts the value of the state’s pine plantations at $617 million a year when both the direct value of products and flow-on effects are taken into account.

The report, funded by Forest and Wood Products Australia and conducted by the University of Canberra and EconSearch, also found the plantations generated 863 jobs to the point of primary processing – and most forestry jobs are in regional WA.

Van Etten, for one, isn’t advocating for an end to pine plantations.

“They have many benefits, not just to cockatoos, of course,” he says.

“A well-managed pine plantation is an effective supply of wood, which means we're not having to harness native forest to supply our demand for timber.”

Van Etten also points out that the land has already been cleared, and there are benefits to planting trees rather than having large areas of agriculture.

“They can be important for stopping soil erosion, reducing dryland salinity and all sorts of things,” he says.

“There is definitely a role for established plantations, and I think the conflict around pine invasion can be easily managed.”

The living dead

But there’s no denying the pines have come at a cost.

Froend says today many of the wetlands are so degraded that little of the original vegetation remains.

“In some cases, there are remnant wetland trees that are standing but they are the living dead, remnants of populations that are not regenerating,” he says.

“We no longer have shallow water tables, no longer have the long periods of flooding or inundation that these species require, so the populations of these trees are gradually declining and eventually they will be lost.”

Stock says previous attempts to restore the Banksia woodland have proved expensive and prone to failure.

“What is very apparent these days is that you can't knock something over and put back what was there before,” he says.

Instead, he believes we should slow the clearing of Banksia woodland, retain some pine plantations and plant crops such as macadamias that could provide an alternative food source for the cockatoos.

Froend agrees the change is unequivocal.

“It is the best case study in Australia, and one of the best in the world, in terms of the multifaceted impacts… on groundwater-dependent systems and entire landscapes, as a consequence of our own actions,” he says.

Despite years of warnings, Froend believes we still don’t have the balance right on the Gnangara Mound.

“We see governments often vacillate when they get recommendations for integrated management of the Gnangara Mound, and there doesn't appear to be any effective change,” he says.

“Carnaby’s cockatoos are still getting rarer and Banksia woodland is protected now but it's still declining due to the drying landscape.”